Add 1 mL of 10% Ammonium hydroxide to standard or sample solution.
Did you try the the method on USP 32, Page 2444.? Mobile phase: 2.0 g of KH2PO4 into 650 mL of H2O, Add 15 mL of 0.5 M Tetrabutylammonium hydroxide in methanol, 7.0 mL of 3N H3PO4, and 270 mL of Methanol. Adjust to pH of 5.0 with 3N of H3PO4 or 6N Nh4OH.
得到澄清溶液: for standard preparation and sample preparation: Add 1 mL of 10% Ammonium hydroxide and dilute to volume with the mobile phase.
USP recommend internal standard method calculation, however it's fine to use external standard calculation.
isotope Folic acid as reference standard. CID channels of m/z 442 → m/z 295 and m/z 447 → m/z 295, which are the neutral glutamyl loss of the [M+H]+ ions of folic acid and 13C5-folic acid, respectively. SIM mode for monitoring the [M+H]+ ions of folic acid and 13C5-folic acid at m/z 442 and 447.
SPE: we used the Phenyl cartridge or general C18 cartridge with a good recovery. As for the SAX SPE, (I heart some co-worker complained before), it needs further cleanup.
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